Tricellaria dubia Silén, 1941

(Fig. 26; Table 24)

Tricellaria dubia Silén, 1941: 78, figs 93–95.

Material examined. Paratype UPSZTY 2475, Okinose, Sagami, Japan; depth 150–600 m. Leg. Prof. S. Bock 1914. The material consists of three small colony fragments: A, two internodes (Fig. 26A); B, two internodes (Fig. 26B–F); C, three internodes, two of which incomplete (Fig. 26G, H).

Description. Colony erect, jointed, fixed to the substrate by smooth rhizoids (Fig. 26A); internodes straight, formed by 6–8 autozooids between bifurcations and joints at the basis of the branch.

Autozooids club-shaped, curved, elongate (mean L/ W 2.85), distinct, separated by shallow furrows, arranged in alternating biserial rows (Fig. 26A, B).

Opesia elliptical occupying about two-fifths of zooidal length (mean OpL/ZL 0.45) outlined by a raised, beaded rim of cryptocyst (Fig. 26E); smooth cryptocyst forming a narrow (c. 15–30 µm), slightly depressed band proximally, steeply sloping laterally and distally (Fig. 26F); scutum arising from a stout base (15–20 µm in diameter) placed on the inner edge of opesia at about its mid-length or proximal third, irregularly rounded, 60–110 × 50–90 µm, usually more developed proximally than distally, and often with an asymmetrical projection at the distal outer corner (Fig. 26C–E); two articulated spines on the outer edge of each autozooid, the distal spine short and thin (35–85 µm long and 12–20 µm in diameter), the distolateral one very long and robust (at least 415–485 µm long and 25–40 µm in diameter), often curved towards the front of the branch (Fig. 26A–C, G).

Dorsal side smooth with a median shallow furrow marking zooidal boundaries (Fig. 26G, H).

Avicularia absent. Ovicells not observed.

Remarks. Silén (1941) mentioned the absence of ooecia in the holotype (i.e. SMNH-Type-9376) but remarked their presence in paratypes from the Bonin Islands (locality 34). Specimens examined here, which are paratypes from locality 29, also lack ooecia. They are described as large, a little elongate with a shallow depression distally in the front, without a fenestra. Locality numbers refer to the list provided in Silén (1941).